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Sunday, March 11, 2012

Tim Severin's Bamboo Raft

Like his earlier book The Brendan Voyage, which we have discussed previously, Tim Severin's The China Voyage: Across the Pacific by Bamboo Raft is above all a great adventure. In it, he tells of his fascination with the legend of the Chinese navigator Hsu Fu, who, in 218 BC, set sail on a bamboo raft from China's Pacific coast heading east, and found, and possibly settled in, new lands. Lending credence to the story was the work of some well-respected modern anthropologists who theorized that South America had been settled, if not populated, by Chinese sailors on bamboo rafts. (The theory proceeds that the balsa-log rafts of South America were a local adaptation of the Chinese raftbuilding technology.) While the evidence for this pre-Colombian contact is not well-accepted, there's enough fragmentary and circumstantial evidence to lift the theory above the realm of crackpot pseudo-archaeology and make it an intriguing possibility to contemplate.

Hsu Fu, from The China Voyage by Tim Severin. (Please pardon the gutter between the two pages, which I couldn't avoid when scanning.) Click to enlarge.

In The China Voyage, Severin never seems to buy wholeheartedly into the theory, but he is willing enough to accept it as a possibility, to the extent of making it the motive for another of his voyages on antique boat types. If, he reasoned, he could demonstrate that a bamboo raft was capable of crossing the Pacific, then at least the theory could not be rejected on the basis of technical infeasibility.Unable to find any native builders of bamboo rafts in China in the early 1990s, he looked further afield and found the craft still being practiced in Sam Son, Vietnam. The Vietnamese rafts, however, were rather small and used for coastal fishing. But Chinese seagoing rafts were pretty well documented by Europeans even into the 20th century, so Severin had designer Colin Mudie use what was known about them to draw plans for a raft 60 feet LOA by 15 feet in beam. Working with the Vietnamese craftsmen, Severin had them build the raft to Mudie's plans, using their own native skills.Severin's raft, which he named Hsu Fu, is shown above. The deck was composed of three layers of large-diameter bamboo, lashed together with split rattan. The bamboos were also lashed to several curved timber frames which game the boat a slight amount of deadrise. The bamboos were bent upward somewhat at the bow, helping the boat rise to waves. Rattan hogging trusses above both gunwales were intended to stiffen the structure fore-and-aft, but in fact they seem to have been largely ineffective, and they broke frequently.

Deck layout of Hsu Fu.

Propulsion was three Chinese lugsails, each (of course) on its own mast, totaling 800 square feet. Several daggerboards could be raised and lowered between bamboos, both to limit leeway and to alter the direction of sail by changing the center of lateral resistance. A steering oar was also used. Even so, the raft's windward sailing ability was severely limited.Severin praised Hsu Fu's seakindly motion, however, saying that it was the most stable boat he had ever sailed on. With essentially no freeboard at all, waves actually washed through the raft's structure, between the bamboos. And while this made for a constantly wet ride, it also meant that, to an extent, the vessel did not follow the surface of the sea as it sloped this way and that, but remained more nearly level instead.The structure was also flexible. With very little to stiffen it fore-and-aft, the only way that a craft made of such materials could survive was by flexing as it rode the waves. (I acknowledge that this contradicts the notion of stability as described in the previous paragraph, and this is due to my own lack of understanding. Perhaps it was the short choppy stuff that passed through the structure, while the deck conformed overall to the shapes of the swells.) The raft rode through several bad storms and, except for being constantly wet, the crew were fairly comfortable, because of the raft's easy motion. Severin, his crew and Hsu Fu traveled 5,500 miles in 105 days at sea, making it most of the way across the Pacific before the raft began to break up due to the rattan lashings rotting. (They were about 1,000 miles from landfall in the Americas when they abandoned ship to be picked up by a passing vessel.) Even so, Severin felt that the experiment was successful in demonstrating the feasibility of a bamboo raft-bound migration to the western hemisphere, noting some mitigating factors, including that his expedition began in Vietnam, which added several hundred miles to the voyage compared to the theoretical start in China. My personal conclusion is that while it wasn't great science, it was a great adventure in a well-written book.We'll look at some more Chinese bamboo rafts in the next post.